The present invention relates to a fluid friction clutch or drive that is especially suitable for driving a motor vehicle fan.
Such fluid friction clutches are known in the prior art and are used for radiator fans or as drives per se, in order to permit sufficient dissipation of heat from the thermal energy generated by an internal combustion engine, for example. Such fan clutches are used in particular for vehicles in the medium power range, such as transporters, off-road vehicles, lightweight goods vehicles and agrarian applications.
In addition to electrically actuated fan clutches, use is also made of thermally actuated fluid friction clutches which have a bimetallic valve and which have storage chambers or reservoirs only on the secondary side. However, this design has control problems at low rotational speed and in the case of rapid engagement of the clutch and/or its starting characteristics. In particular, this is disadvantageous in the case of vehicles with gasoline engines in which the ratio between nominal rotational speed and idling speed of the motor assumes relatively high values.
Furthermore, so-called “fan boom” or “morning sickness” problems are known. These are caused in particular by the fact that the transmission region of the clutch is relatively highly filled with oil when the engine is idling (fan boom) or when the engine is cold started (morning sickness) and, as a result of relatively high engine rotational speeds and the associated fan clutch engagement, the fan causes unnecessary and/or unpleasant fan noise.